Invisible inks are part of the ancient science of steganography where hidden messages cannot be read by anyone other than the intended recipient, but also that no one else knows the message is even being sent. Invisible ink has been used since ancient times to produce steganographic writings. A variety of invisible ink substances have been known for centuries with varying success, including fruit juices and cobalt salts that could be developed and detected through heat or light. While invisible ink has largely been replaced as an espionage tool by cryptography, these materials are still used for security marking and amusement.
It is still the case, just as in ancient times, that writing with invisible ink involves an instrument separate from the visualization equipment. This separation is inconvenient during writing as intermediate visualization of the writing is impractical and there is a tendency to lose either the writing instrument or the visualization equipment. While a conventional security pen affords all the convenience of a visible writing instrument, ultraviolet and black light sources have remained inconveniently large to carry in conjunction of a conventional security marker. Thus, there exists a need for a writing system having a visualization element integrated with an invisible ink writing instrument.